Earth's
recent warming trend
might in part be due to a lack of starlight reaching our planet, a new study
suggests. But other scientists are not so sure.
According
to a theory proposed a decade ago, when a star explodes far away in the Milky Way, cosmic
rays--high-speed atomic particles--go through the Earth's atmosphere and produce ions and
free electrons.
The
released electrons act as catalysts and accelerate the formation of small
clusters of sulfuric acid and water molecules, the building blocks of clouds.
Therefore, cosmic rays would increase
cloud cover on Earth, reflecting sunlight and keeping the planet relatively
cool.
However,
because the Sun's
magnetic field--which shields the Earth from these rays--doubled in intensity
during the last century, there has been a reduction in cloudiness, a possible
contributor to Earth's
warming.
Scientists
at the Danish National Space Center mimicked chemistry of the lower atmosphere in a large
reaction chamber. They created a mixture that contained gasses at realistic
concentrations and used an ultraviolet lamp to act as the Sun.
Microscopic
droplets, precursor to clouds, started floating in the air of the reaction
chamber.
"We were
amazed by the speed and efficiency with which the electrons do their work of
creating the building blocks for the cloud condensation
nuclei," said team leader Henrik Svensmark, Director of the Center for
Sun-Climate Research at the Danish National Space Center. "This is a completely new result
within climate science."
The results
however, may not transfer to natural conditions outside the controlled
laboratory environment.
"Studies
that have evaluated the claims that global cloud cover is related to changes in
cosmic rays find that if you re-examine this matter outside of the brief period
which they used, the relationship falls apart," said Raymond Bradley director
of the Climate System Research Center at the University of Massachusetts. Bradley was not involved with the
study.
The
researchers agree that further study is needed to estimate the contribution of
this mechanism to the recent warming of the Earth's atmosphere and oceans.
This work
does not mean that there is no human influence on climate, Svensmark told LiveScience.
"But it might be necessary to revaluate the climate sensitivity to carbon
dioxide."
The study
was detailed online this month in the Proceedings of the Royal Society A.
This
article is part of SPACE.com's weekly Mystery Monday series.
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